1. Field
The present disclosure relates generally to composite structures and, in particular, to composite laminates. Still more particularly, the present disclosure relates to a method and apparatus for improving the through-thickness strength of a composite laminate using a filament network.
2. Background
A composite laminate is formed by one or more composite layers, which are also referred to as plies or lamina. Each composite layer includes a reinforcement material and a matrix material. The reinforcement material may take the form of, for example, fibers, which may be oriented in a single direction to make the composite layer unidirectional or in two directions to make the composite layer bidirectional. The matrix material may take the form of, for example, a resin.
Fiber bundles may be laid up in layers to form a reinforcement layup, which may be referred to as a preform. The preform may be a referred to as a wet preform when the fiber bundles have been pre-impregnated with resin that has been partially cured for handling or a dry preform when no resin is present. Resin is infused within the spaces between the fiber bundles of the preform to form an integrated preform. The integrated preform may be partially cured to form a partially cured composite laminate or fully cured to form a fully cured composite laminate. A carbon fiber-reinforced polymer (CFRP) laminate is an example of one type of composite laminate.
In some cases, an undesired inconsistency may develop within the composite laminate. An undesired inconsistency is an inconsistency that is outside of selected tolerances or beyond some selected threshold for the inconsistency. An undesired inconsistency may take the form of, for example, a crack, a thermally-induced crack, a notch, a delamination, or some other type of inconsistency that is outside of selected tolerances.
The ability of a composite laminate to absorb energy in the presence of an undesired inconsistency, while still performing within selected tolerances, is commonly referred to as the notch toughness of the composite laminate. Improving the notch toughness of a composite laminate, while still allowing a resin to be effectively infused between and around the fibers, may be more difficult than desired. Some currently available methods for improving the notch toughness of a composite laminate may reduce the performance of the composite laminate in other areas.
For example, one currently available solution includes laying up a sheet of discontinuous fibers between each pair of composite layers in the composite laminate. However, this type of solution improves the notch toughness of the composite laminate but reduces the resistance of the composite laminate to the formation of undesired inconsistencies.
Other currently available solutions include Z-pinning, stitching, and tufting. Z-pinning includes forcing pins through the reinforcement layup or the uncured preform in a Z direction. Stitching and tufting include threading fibers through the reinforcement layup or the uncured preform in the Z direction. However, these types of solutions may still reduce the resistance of the composite laminate to the formation of undesired inconsistencies, cause undesired effects to the fibers, and limit the sizes and positioning of the pins or threads that can be used. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues.